1. Field of the Invention
The present invention relates to a method and device for damping out vibrations and sounds from flexible stuctures by treating the structure with an actively-controlled constrained layer.
2. Description of the Related Art
Passive surface treatments have been extensively utilized, as a simple and reliable means, for damping out the vibration and sound of a wide variety of flexible structures (Cremer, Heckl and Ungar 1988). Such surface treatments rely in their operation on the use of visco-elastic damping layers which are bonded to the vibrating structures either in an unconstrained or constrained configuration as shown in FIGS. 1 and 2, respectively.
Under cyclic loading, constrained damping layers experience shear strains which are much larger than those encountered in unconstrained damping layers (Nashif, A., D. Jones and J. Henderson 1985). Accordingly, the constrained damping layers are capable of dissipating higher vibrational energies and, in turn, achieving higher damping ratios than their counter-parts: the unconstrained damping layers. Higher damping ratios can also be attained, over a broad range of temperatures and frequencies, through the use of multilayer damping (Asnani and Nakra 1976). Higher damping ratios are obtained, however, at the expense of adding considerable weight to the vibrating base structures. This poses serious limitation to their use for many applications where the weight is of critical importance.
It is therefore an object of this invention to introduce a new class of actively-controlled constrained layer damping (ACLD) treatment which can have high energy dissipation-to-weight characteristics as compared to conventional constrained or unconstrained damping layer configurations.